Catalytic alkylation of phenol



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This invention relates to the preservation of rubber, and more particularly to the provision and use of a new class of nonstaining or nondiscoloring age resistors for rubber.

.Rubber is subject to deterioration from many sources,

such as sunlight, ozone, atmospheric oxygen, presence of heavy metals, etc. Both cured and uncured natural and synthetic elastomers are subject to deterioration. Deterioration in cured stock may likewise vary with the type of stock, the state of cure, the amount of surface exposed and the temperature at which the rubber is being used. An ideal antioxidant would be one which would protect rubber from deterioration regardless of kind, in the cured or uncured state, no matter where used. Since no such antioxidant has been discovered, compromises must be made in the selection of an antioxidant for use in rubber.

With the increasing demand for white or light-colored rubber articles there arose a need for antioxidants which would not discolor rubber or stain objects in contact with rubber. The older antioxidants produced very bad discoloration and staining. Certain alkylated phenols have been found to be antioxidants which produce little discoloration or staining. While many phenols have some antioxidant activity, there is a great difference between various phenols as to their efiectiveness and also as to their degree of discoloration of rubber goods.

The effectiveness of a phenolic antioxidant will vary with the degree of alkylation, the type of alkyl groups present and the location of the substituent alkyl groups. Furthermore, the vapor pressure of the phenolic molecule is of particular importance for certain uses, i.e. for high temperature uses and for uses wherein large rubber surfaces are exposed. Again compromises may have to be made, for example, a good antioxidant may be too volatile for general usage while, on the other hand, a nonvolatile material may be a poor antioxidant.

According to the present invention, a class of phenols has been discovered which exhibit unusual and unexpected antioxidant activity, and which are relatively nonvolatile. They exhibit a high degree of protection for rubber against sunchecking and against atmospheric oxygen, produce little or no discoloration in rubber, and are also nonstaining. Furthermore, they are derived from cheap raw materials and hence possess an economic advantage over most antioxidants of this general class. The customary phenolic antioxidant is quite volatile because of the difficulty of effecting heavy alkylation, most phenolic antioxidants being cresol derivatives. Now, it has been found that, by selecting the alkyl substituents carefully and by reacting them with phenol in a stepwise order, a class of antioxidants may be produced easily and economically which has low volatility and which displays excellent antioxidant properties. The age resistors of this invention which can be produced in this manner, are phenols having at least two unlike tertiary alkyl radicals attached to the ring, at least one of the radicals being selected from the group consisting of tertiary octyl and tertiary nonyl radicals and at least one being selected from the group consisting of tertiary butyl and tertiary amyl radicals.

In the practice of this invention, the alkylated phenolic compounds can be made by reacting phenol with an olefin selected from the group consisting of tertiary octenes and tertiary nonenes and then with another olefin se- Patented Mar. 14, 1961 lected from the group consisting of isobutylene and tertiary amylenes. Mixtures of octenes and/or nonenes and mixtures of isobutylene and/or amylenes can be used, if desired.

Many alkylated phenols have not proved to be good antioxidants. This may be due to the fact that the action of the OH group must be inhibited in order to have a good antioxidant. For this purpose large groups ortho to the hydroxyl are desirable. The size of these groups is limited, however, by the fact that heavy chains are not easily attached and by the fact that the composition would become too costly and difficult to make to use as an antioxidant if the chains were too large.

It has been discovered that certain phenols having tertiary groups in the ortho and para positions are superior antioxidants, the best antioxidants being tri-tertiary alkyl substituted phenols. By the practice of this invention, the maximum effect is obtained by securing tri-tertiary substitution of the phenol nucleus with octyl, nonyl, butyl or amyl groups. In order to obtain the desired antioxidants the heavier tertiary olefin is reacted with phenol first and thereafter the product of that reaction is reacted with the lighter tertiary olefin.

While the invention includes the isolation and use of the individual compounds, the composite reaction products are preferred as age resistors, since their use saves the additional costs of purification or separation. The products may be produced from pure compounds or from mixtures of compounds.

For best results the reaction temperature during alkylation will ordinarily be maintained within a range of 50 C. to 150 C. If the temperature is too high, the alkylation catalyst may become a catalyst for dealkylation. During the second stage of the alkylation process, it is often desirable to maintain the temperature below C. in order to prevent dealkylation and in order to obtain more complete alkylation. The temperature will of course vary with variations in customary reaction conditions such as, for example, pressure, catalyst used, etc.

In the practice of the invention, one or more of the customary acidic alkylation catalysts is used to activate and accelerate the reactions. For example, sulfuric acid, benzene sulfonic acid, toluene sulfonic acid, activated clays, stannic chloride, ferrous chloride, boron trifluoride, zinc chloride, the ferrous and ferric halides, the stannous and stannic halides, aluminum halide and aluminum oxide will catalyze the reactions. Usually, concentrated sulfuric acid is used as the alkylation catalyst. However, it has been noted that reaction products of this invention produced by a concentrated sulfuric acid catalytic system exhibit a pronounced yellow color which is carried over into the rubber when synthetic rubbers containing them are made by emulsion polymerization. Such polymers are often undesirable from the standpoint of sales appeal even though the color does not carry over into white or light colored vulcanizates. It has been discovered that this problem of coloration can be overcome by using particular combinations of the herein-disclosed acidic alkylation catalysts. In particular, it has been discovered that combinations of acid-activated clay and sulfuric acid are effective catalysts which provide non-discolored polymers. Tests have shown that the clay does not merely absorb the color as might be expected because known acidactivated bleaching clays have failed to remove color from sulfuric-acid catalyzed reaction products of this invention. The catalyst may be comprised of a mixture of an acid-activated clay and sulfuric acid in a ratio of about 1 to 7 parts by weight of clay to 1 part by weight of acid. The-clay may be dry or it may contain from O to 15% by weight of water. Also the catalysts may be used in sequence, if desired, the clay being used in an amount of from 3 to 15 grams per mol of phenol to activate the first alkylation step and the sulfuric acid being added in an amount of from 0.1 to 1.0% by weight, based on the Weight of reactants, to the mixture to activate the second step.

Although useful in preparing any of the reaction products disclosed herein, when nonylenes are used as the olefin in the first reaction step and isobutylene is used as the olefin in the second reaction step, it has been discovered that best results are achieved by using an acidactivated clay as the catalyst in an amount of about 3 to 15 grams per mol of phenol to catalyze the first step of the reaction and thereafter adding from 0.1 to 1.0% by weight, based on the weight of reactants, of substantially concentrated sulfuric acid to catalyze the second step of the reaction.

The products of this invention, produced by the catalyst systems claimed herein and further described in the following examples, were tested for color by incorporating 2 parts by weight of antioxidant in 100 parts by weight of rubber as follows:

Twenty-five grams of a 6% sodium oleate Water solution were heated to 140 to 160 F. and thereafter added with stirring to 25 grams. of the antioxidants to provide an emulsion. Then 1.34 grams of the 50% emulsion were added to 200 grams of SBR hot latex containing about 17% rubber solids comprised of a copolymer containing about 75% by weight of butadiene and 25% by Weight of styrene. This is aratio of approximately 2 parts by weight of antioxidant to 100 parts by weight of rubber. The sodium oleate solution was used only as an emulsifying agent to aid dispersion of the antioxidant in the latex. Obviously, any other emulsifying agent may be used for this purpose, as Well-known in the art. Latex, containing the antioxidant, was poured into 100 milliliters of a 10% sodium chloride solution and thereafter coagulated with dilute sulfuric acid wherein the pH was reduced to about 3 to 4. The crumb rubber was washed thoroughly with water and oven-dried for 16 hours at 158 F- Thereafter, the rubber was examined visually for discoloration and compared to a control containing no antioxidant.

In the following table, the antioxidant used was the reaction product of phenol, tri-propylene, and isobutylene, as described in Example 1, the only change being thevariations in the catalysts shown in the table.

TABLE 1 Quantity/mol Phenol Catalyst Color of Final Product Almost white. Very yellow.

H H H r e-asu suprpr'sn OOOOOOOOOOOGOOOOO The catalyst will ordinarily be used in an amount of at least 0.5% of the total weight of reactants, i.e., phenol plus olefins, but larger amounts of catalyst, for exampic, up to 10.0% by weight of the reactants, are also satisfactory.

By the processof the invention a phenolic antioxidant can be obtained which is substantially trialkylated with 4: tertiary alkyl radicals. In order to obtain the desired alkylation, the phenol must be reacted with the tertiary octene or tertiary nonene as the first step in the process, the use of at least one mol of tertiary octene or tertiary nonene per mol of phenol being necessary in order to obtain at least monoalkylation of a substantial portion of the phenol molecules. When only'one mol of tertiary octene or tertiary nonene is used in'the first'step, it becomes necessary to use at least two mols of a tertiary butene or a tertiary pentene in the second step in order to obtain the desired trialkylation. It is preferred to use more than one mol of the tertiary octene or tertiary noneneper mol of phenol in the first step of the process because it is desirable to obtain phenolic reaction products having more than one position on the phenolic ring substituted with the heavier alkyl radicals. Still more preferred is the use of at least two mols of the tertiary octene or nonene. More than two mols of tertiary octene or tertiary nonene per mol of phenol can be used, in the first step in order to insure that a substantial portion of the phenolic reaction products will be dialkylated with tertiary octyl or tertiary nonyl radicals. At least one mol of isobutylene and/ or tertiary amylene must be used and the total amount of olefinmust be at least three mols per mol of phenol.

It is possible to obtain a phenolic antioxidant reaction product in which a major portion of the phenolic moleeules will be dialkylated with either a tertiary octyl or a tertiary nonyl group and monoalkylated with either a tertiary butyl or a tertiary amyl group. Because of chemical selectivity, one tertiary octyl or tertiary nonyl group will normally attach to the position para to the hydroxyl and the other ortho to the hydroxyl. This would leave the other ortho position available for a tertiary butyl or tertiary amyl group. If sufiicient octylene or nonylene is not used for substantially complete dial= kylation, the tertiary octyl or tertiary nonyl radical will attach to the para position, leaving the two ortho positions available for the tertiary butyl or tertiary amyl groups. These two types of compounds account for a substantial portion of the reaction product, i.e. at least 60% of the total composition, and under proper reaction conditions will amount to about to of the total composition. Other compounds which can be present in the reaction product in varying but minor amounts are '(l) the disubstituted phenols in which both substituents are di-tertiary octyl (or nonyl) or di-tertiary butyl (or amyl) or in, which one substituent is tertiary octyl (or nonyl) and the other substituent is tertiary butyl (or amyl) and (2) the tri-Substituted phenols in which all three substituents are tertiary octyl (or nonyl) on the one hand or tertiary butyl (or amyl) on the other.

Preferably, an excess of the heavier olefin isused, i.e., more than two mols of olefin for each mol of phenol, thus insuring a major proportion of dialkylation with the heavier reactant. It is thus possible to obtain up to about 50% to 75% of the reaction product comprised of phenolic molecules having dialklation with octyl or nonyl groups and monoalkylation with butyl or amyl groups. The remaining reaction products will be various proportions and combinations of other diand tri-tertiary alkyl phenols with alkylation in the para and ortho positions, almost no, alkylation occurring in the meta positions. An' excess of tertiary butyleneor amylene in the secondstep tends to promote complete reaction to the tri-substituted compounds.

The preferred antioxidant composition of this invention is a mixture of tertiary alkylated phenols which. have the structural formula 5 wherein at is an integer ranging from 2 to 3, n is an integer ranging from to 3 but not exceeding the value of x, wherein R is selected from the group consisting of tertiary butyl and tertiary amyl and R is selected from the group consisting of tertiary octyl and tertiary nonyl, R and R being attached to the benzene ring in the 2, 4 and 6 positions with respect to the hydroxyl group, and wherein a major proportion of said mixture is comprised of tri-tertiary-alkylated phenols wherein two of said tertiary alkyl radicals are selected from the group consisting of tertiary octyl and tertiary nonyl radicals and wherein the third tertiary alkyl radical is selected from the group consisting of tertiary butyl and tertiary amyl radicals.

The reaction product can also be described as a mix- "ture of phenols having the structural formula i l. lit

wherein n and n are integers ranging from 1 to 2, but not totalling more than 3, wherein R is a monovalent radical selected from the group consisting of CH, and C l-I and R is selected from the group consisting of C I-I and C l-I wherein alkylation of the phenolic ring is in the 2, 4 and 6 positions, and wherein a major proportion of said mixture is comprised of tri-tertiary-alkylated phenols wherein two of said tertiary alkyl radicals are selected from the group consisting of tertiary octyl and tertiary nonyl radicals and the third tertiary alkyl radical is selected from the group consisting of tertiary butyl and tertiary amyl radicals.

The preparation of the products of the invention is illustrated by the following examples:

Example 1 Ninety-four grams of phenol, grams of an acidactivated clay and 158 grams of a tripropylene were heated at 130 C. for two hours. The excess tripropylene was then removed at 130 C. by reducing pressure to 15 to 25 millimeters of mercury pressure. The reaction mixture was cooled to 80 C. One gram of H 80 was added and then 117 grams of isobutene were added in one hour. The catalyst was neutralized with aqueous Na CO and the volatiles removed by heating to a column temperature of 160 C. at millimeters of mercury pressure. The yield was 283.0 grams.

Example 2 Example 3 Ninety-four grams of phenol, 158 grams of tripropylene and 10 grams of a dry activated clay were heated at 130 C. for two hours. The reaction mixture was cooled to 80 C. and 1 gram of H 50 was added. Thereafter, 127 grams of isobutylene were added in one hour. The catalyst was destroyed and the volatiles removed as in Example 1. The yield was 301 grams.

Example 4 Ninety-four grams of phenol, 158 grams of tripropylene and 10 grams of an activated clay containing 15% moisture were heated at 130 C. for two hours. The unreacted tripropylene was removed at 130 C. by reducing the pressure to 15-25 millimeters of mercury pressure. The reaction mixture was cooled to C. and 1.0 gram of H 50 was added. One hundred and twelve grams of isobutylene were added between 80 and C. in one hour. The catalyst was destroyed and the volatiles removed. The yield was 290.0 grams.

Example 5 Nine hundred and forty grams of phenol, 1,575 grams of mixed nonenes and grams of an acid-activated clay containing 15% moisture were heated at C. for three hours. The unreacted nonenes and phenol were removed by heating to C. at a pressure of 15 millimeters of mercury pressure. The mixture was cooled to 80 C. and 10 grams of concentrated sulfuric acid were added. Twelve hundred and fifty-seven grams of isobutene were added in 3 /2 hours between 80 and 85 C. Twenty grams of Na CO dissolved in water were added to destroy the catalyst. The whole was then heated to 180 C. at 18 millimeters of mercury pressure to remove volatiles. The yield as 2,875 grams.

Similar compounds have been prepared as in Examples l-5 except that diisobutylene has been used instead of a nonene. Also, similar compounds have been prepared as in Examples 1-5 wherein diisobutylene has been used instead of a nonene and an amylene has been used instead of isobutylene.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

This application is a continuation-in-part of Serial No. 379,089, filed September 8, 1953.

I claim:

1. The method which comprises reacting phenol with from one to two moles of an olefin selected from the group consisting of tertiary octene and tertiary nonene in the presence of from 3 to 15 grams of acid-activated clay per mol of phenol at a temperature of from 50 to 0., adding from 0.1 to 1.0% by weight, based on the weight of the reactants, of sulfuric acid and further reacting the mixture with at least one mole of at least one other olefin selected from the group consisting of isobutylene and tertiary amylene at a temperature of from 50 to 90 C.

2. The method which comprises reacting a tertiary alkyl phenol containing from 1 to 2 tertiary alkyl substituents selected from the group consisting of tertiary octyl and tertiary nonyl with at least one mol of at least one olefin selected from the group consisting of isobutylene and tertiary amylene at a temperature of from 50 to 90 C. in the presence of from 3 to 15 grams of acid-activated clay per mol of the phenol and from 0.1 to 1.0% by weight based on the weight of reactants of sulfuric acid.

References Cited in the file of this patent UNITED STATES PATENTS 2,283,438 Hentrich et al May 19, 1942 2,337,123 Olin et a1. Dec. 21, 1943 2,415,069 Arvin et al Feb. 4, 1947 2,434,833 Ciapetta Jan. 20, 1948 2,560,037 Kitchen July 10, 1951 2,732,408 Foote Jan. 24, 1956 OTHER REFERENCES Stillson et al.: J. Amer. Chem. Soc., vol. 67 (1945), pages 303-307 (5 pages). 

1. THE METHOD WHICH COMPRISES REACTING PHENOL WITH FROM ONE TO TWO MOLES OF AN OLEFIN SELECTED FROM THE GROUP CONSISTING OF TERTIARY OCTENE AND TERTIARY NONENE IN THE PRESENCE OF FROM 3 TO 15 GRAMS OF ACID-ACTIVATED CLAY PER MOL OF PHENOL AT A TEMPERATURE OF FROM 50 TO 150* C., ADDING FROM 0.1 TO 1.0% BY WEIGHT, BASED ON THE WEIGHT OF THE REACTANTS, OF SULFURIC ACID AND FURTHER REACTING THE MIXTURE WITH AT LEAST ON E MOLE OF AT LEAST ONE OTHER OLEFIN SELECTED FROM THE GROUP CONSISTING OF ISOBUTYLENE AND TERTIARY AMYLENE AT A TEMPERATURE OF FROM 50 TO 90*C. 